1. Field of the Invention
The present invention relates to an aluminum oxide sintered product and a method for producing such an aluminum oxide sintered product.
2. Description of the Related Art
Electrostatic chucks have been used for holding wafers in semiconductor manufacturing equipment. Such an electrostatic chuck includes an internal electrode for applying a voltage and a dielectric layer placed on the internal electrode. When a wafer is placed on the dielectric layer and a voltage is applied to the internal electrode, an electrostatic attractive force is produced between the wafer and the dielectric layer. There are electrostatic chucks employing a monopolar system in which one internal electrode is contained and electrostatic chucks employing a bipolar system in which a pair of (that is, two) internal electrodes are contained so as to be spaced apart from each other. An electrostatic chuck employing the monopolar system is configured to produce an electrostatic attractive force by applying a voltage between the internal electrode of the electrostatic chuck and an external electrode placed outside the electrostatic chuck. An electrostatic chuck employing the bipolar system is configured to produce an electrostatic attractive force by applying a voltage to a pair of internal electrodes. Referring to FIG. 11, such electrostatic chucks are broadly divided into a Johnson-Rahbeck type in which a wafer is attracted with a Johnson-Rahbeck force produced using a dielectric layer having a volume resistivity of about 108 to 1012 Ω·cm, and a Coulomb type in which a wafer is attracted with a Coulomb force produced using an insulator (having a volume resistivity of more than 1016 Ω·cm) as a dielectric layer. The Johnson-Rahbeck type electrostatic chuck provides a high attractive force; however, it requires an expensive power supply having a high current-carrying capacity and small current passes through the wafer due to leakage current, which can electrically damage integrated circuits fabricated in the wafer. For these reasons, the Coulomb type electrostatic chuck, which causes less leakage current, has been often employed in recent years. However, the Coulomb type electrostatic chuck provides an electrostatic attractive force smaller than that in the Johnson-Rahbeck type electrostatic chuck, which is a problem. To solve this problem, studies have been performed on how to control the volume resistivity of a dielectric to be about 1×1014 Ω·cm to thereby achieve an increase in attractive force and a decrease in leakage current. For example, in Patent Document 1, the volume resistivity is adjusted by firing a mixture containing aluminum oxide and conductive silicon carbide. In Patent Document 2, the volume resistivity is adjusted by firing a mixture containing aluminum oxide and conductive magnesium oxide and titanium oxide.